Scale Control for Long Term Well and Facility Preservation

Oilfield scale and corrosion at oil and gas wells and topside facilities are well known problems. There are many studies towards the control and mitigation of scaling risk during production. However, there has been limited research conducted to investigate the effectiveness of scale control approaches for the preservation of wells and facility during a potential long term shut-in period, which could last more than 6 months. Due to low oil price and harsh economic environment, the need to shut-in wells and facilities can become necessary for operations. Understanding of scale control for a long term period is important to ensure both subsurface and surface production integrity during the shut-in period. The right strategy and treatment approaches in scale management will reduce reservoir and facility damage as well as the resulting cost for mitigation. In this paper, we will review and assess the scale risk for different scenarios for operation shut-in periods and utilize laboratory study to improve the understanding of long-term impact and identify appropriate mitigation strategy. Simulated brine compositions from both conventional and unconventional fields are tested. Commercially available scale inhibitors are used for testing. Various conditions including temperature (131-171 °F), saturation index (1.28-1.73), pH (7.04-8.03) and ratio of scaling ions are evaluated. The tested inhibitor dosage range was 0-300 mg/L. Inhibitor-brine incompatibility was also investigated. Sulfate and carbonate scales such as barium sulfate, strontium sulfate and calcium carbonate are studied as example. This paper will provide an important guidance for the management of well shut- in scenarios for the industry, for both conventional and unconventional fields. Performance of two scale inhibitors for same water composition are demonstrated. The efficiency of scale inhibitor #2 is lower than that of inhibitor #1. A linear correlation is observed for long term scale inhibitor performance in this case. Protection time is thus predicted from data collected from the first 8-week experiments. The predicted protection time at 250 mg/L of inhibitor A and B is 100 weeks and 16 weeks respectively. The actual protection time will be compared to the predicted value. The inhibitor-rock interaction has also been preliminarily studied. The effects of inhibitor adsorption onto formation rock should be considered for chemical treatment design and performance/dosage optimization. This study provides novel information of scale control in a much longer time frame (up to 6 months). Various parameters may have effects on their long term control. Results will benefit the chemical selection and evaluation for long term well shut-in scenario. In addition, brine-inhibitor compatibility is evaluated simultaneously.

FATTY LIVER DYSTROPHY MODELING BY USING STRONTIUM SULFATE

In recent years, the problem of the increasing number of the hepatobiliary system disorders has acquired particular importance for veterinary medicine. These disorders have negative impact on normal physiology of an animal's body. It is important to continue the search for effective hepatoprotective agents. To test the pharmaceutical activity of new drugs, methods of modeling hepatopathies are constantly being improved. The study suggested a model of fatty liver dystrophy using strontium sulfate.

Controlled Growth of Strontium Sulfate Particles in Aqueous Solution: Inhibition Effects of a Bubble Column Evaporator

In the oil industry, strontium sulfate (SrSO4) scale deposits have long plagued oilfield and gas production operations. This remains an unsolved problem. We here show how the bubble column evaporator (BCE) can be used to control aqueous precipitation from salt solutions. Mixtures of strontium nitrate and sodium sulfate in the BCE system were used to precipitate strontium sulfate at different degrees of supersaturation. The effectiveness of the BCE system was compared to standard mechanical stirring. The precipitation of strontium sulfate in both processes was monitored through turbidimeter, particle counting, Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The results show that the BCE system has a significant inhibition effect and so can be used to control precipitation growth rate, even from supersaturated solutions. This remarkable effect also provides new insights into mechanisms of crystallisation, of bubble interactions and mineral flotation.

A Semiempirical Model for Barium-Strontium-Sulfate Solid Solution Scale Crystallization and Inhibition Kinetics at Oilfield Conditions

Summary Scale inhibitors have been widely used as one of the most efficient methods for sulfate-scale control. To accurately predict the required minimum inhibitor concentration (MIC), we have previously developed several crystallization and inhibition models for pure sulfate scales, including barite, celestite, and gypsum. However, disregarding the wide existence of barium-strontium-sulfate (Ba-Sr-SO4) solid solution in the oil field, no related models have been developed that would lead to large errors in MIC determination. In this study, the induction time of Ba-Sr-SO4 solid solution was measured by laser apparatus with or without different concentrations of scale inhibitor diethylenetriamine penta(methylene phosphonic acid) (DTPMP) at the conditions of barite saturation index (SI) from 1.5 to 1.8, temperature (T) from 40 to 70°C, and [Sr2+]/[Ba2+] ratios from 0 to 15 with celestite SI < 0. The results showed that the Ba-Sr-SO4 solid solution’s induction time increases with the [Sr2+]/[Ba2+] ratio at a fixed barite SI, T, and DTPMP dosage. That means the MIC will be overestimated if it is calculated by the previous semiempirical pure barite crystallization and inhibition models without considering the presence of Sr2+. To resolve such deviations, the novel quantitative Ba-Sr-SO4 solid solution crystallization and inhibition models were developed for the first time. The novel models are in good agreement with the experimental data. They can be used to predict the induction time and MIC more accurately at these common Ba2+ and Sr2+ coexisting scenarios. The observations and new models proposed in this study will significantly improve the barite scale management while Ba2+ and Sr2+ coexist in the oil field. NOTE: Supplementary materials are available in support of this paper and have been published online under Supplementary Data at https://doi.org/10.2118/205367-PA.

Reusable Sensor for Strontium Sulfate Scale Monitoring in Seawater

The onset of scaling in oil pipelines can halt or drastically reduce oil production, causing huge financial losses and delays. Current methods used to monitor scaling can take weeks, while the scaling process only takes few hours. The proposed sensor is designed for online monitoring of strontium ions concentration in seawater as an early scaling indicator. The sensor operates in the GHz range by probing the shift in the resonance frequency due to changes in the ionic concentrations of the medium. The results show selective sensitivity to changes in the strontium ions concentration even in the presence of many other ions found in seawater. The measured sensitivity is found to be stable and linear with a detection level of better than 0.08% (0.042 mol/L) of strontium ions in seawater. This work demonstrates a robust GHz sensor for strontium sulfate scale monitoring and early detection, which could be used in the oil industry to prevent huge production losses. These results could also be extended further to target the monitoring of other ions in different industrial sectors.

Analysis of the Causes of Tube and Pipeline Blocking in Sulige Gas Field

A large number of blockage appeared in gas wells and pipeline appeared, which causedplugging, corrosion and the increasing of wellbore pressure difference, and seriously affect thenormal production of gas well of problems. In this paper, the water quality of produced water fromthe severe cases of single wells or pipeline water were analyzed, also include the composition ofblockage and core with the chemical volumetric method (CVM) , X-Ray Diffraction (XRD) and x-rayfluorescence (XFS) method. Meanwhile, the core powder was leached in simulated acid worksolution, and then the leaching solution was analyzed with CVM. The experimental results show thatThe produced water has high salinity, high contents of Ca2+, Ba2+ and Sr2+, low pH value, which leadto corrosion and scaling. The main components of the blockage are acid insoluble strontium sulfate(barium) scale or corrosion product or mixture of corrosion and CaCO3 scaling product. Ca2+, Ba2+and Sr2+ were easy to scale in wellbore or pipeline when they encountered other produced water fromdifferent formation. The Ca2+, Mg2+, Ba2+, Sr2+ and Fe 2+/3+ mainly derived from the dissolution offormation debris in formation water and working fluid (especially acidic working fluid) to reservoirrock, so the salinity of the produced water increased, and the trend of scaling and corrosion alsoincreased with the gas field development.

Study on Source Analysis of the Cation in Produced Water from Sulige Gas Field and Anti-Scaling Measures

A large amount of foreign matter appears in the Sulige gas well, causing blockage and corrosion of the pipeline, increasing the pressure difference in the wellbore and seriously affecting the normal production of the gas well. The gas wells with serious conditions mentioned above were selected to analyze the quality of single well produced water and the composition of blockage and core. Combined with the XRD analysis results of the cuttings, the long-term leaching experiments on the cuttings in different simulated solutions were carried out to study the sources of scaled ions in the gas wells. The experimental results showed that the extracted water from SD6-1 had high salinity and high content of scale ions Ca2+, Ba2+ and Sr2+;the main component of blockage is the acid insoluble strontium sulfate (barium) scale, and contains a small amount of corrosion products. The easily scalable Ca2+、Mg2+、Ba2+ and Sr2+ produced from the dissolution of the core in the formation water or working fluids, especially the acid erosion dissolves. According to the scaling mechanism, two kinds of Sr/Ba scale inhibitor were selected. The results showed that the barium II scale inhibitor performance is relatively good, and at the concentration of 40 mg/L, and the scale inhibition rate was more than 95%. The clogging of a single well can be reduced by adding a scale inhibitor.